Write advantages and disadvantages of prestressed concrete
[3 marks]Differentiate between Pre-tensioning and Post-tensioning
[4 marks]Arectangular concrete beam of cross-section 30cm deep and 20cm wide is prestressed by means of 15 wires of 5mm diameter located 5.5 cm from the bottom of the beam and 3 wires of diameter of 5mm, 3.5cm from the top. Assuming the prestress in the steel as 840 N/mm2, calculate the stressed at the extreme fibers of the mid span sections when the beam is supporting its own weight over a span of 6 m. If a uniformly distributed live load of 6 kN/m is imposed, evaluate the maximum stress in concrete. The density of concrete is 24 kN/m3
[7 marks]Explain the differences of prestressed concrete (PSC) over reinforced concrete (RCC).
[3 marks]Explain the concept of thrust line in PSC sections.
[4 marks]Arectangular concrete bam 250 mm wide and 300 mm deep is prestressed by a force of 500 kN at a constant eccentricity of 60 mm. The beam supports a concentrated load of 68kN at the centre span of 4 m. Calculate the resultant stresses at center span and quarter span for the beam. Neglect the self-weight of the beam.
[7 marks]Aprestressed concrete beam with a rectangular section 150mm wide, 300mm deep supports a uniformly distributed load of 4 kN/m, which includes the self-weight of the beam. The effective span of the beam is 5 m. The beam is concentrically prestressed by cable carrying a force of 180 kN. Locate the position of the pressure line in the beam.
[7 marks]Discuss IS 1343 recommendations for design of prestressed members subjected to bending and torsion.
[3 marks]Enlist different types of flexural failure and explain any one in detail.
[4 marks]Abeam of symmetrical I-section spanning 8 m has flange width of 150 mm and flange thickness of 80 mm respectively. The overall depth of the beam is 450 mm. Thickness of web is 80 mm. The beam is prestressed by a parabolic cable with an eccentricity of 150 mm at the centre of the span and zero at the supports. The Live Load on the beam is 2.5kN/m. (1) Determine the effective force in the cable for balancing the Dead Load1 and Live Load on the beams (2) Calculate the shift of the pressure line from the tendon centre line.
[7 marks]Explain difference between Time dependent and Immediate losses in Prestressed concrete sections.
[3 marks]List the various types of tensioning device used in prestressed concrete.
[4 marks]Apre-stresses beam, 180mm wide and 400mm deep, is prestressed with tendons of 3 wires of 8mm diameter initially stressed to 1200 N/ m2 located at 80mm from the soffit of the beam. Span of the beam is 8m; find the percentage loss of stress in tendons if
Enlis the assumptions of Strain compatibility method
[3 marks]Discuss IS 1343 recommendations for design of prestressed members subjected to shear
[4 marks]Arectangular beam of span 8m and cross section 100mm wide x 250mm deep is prestressed by a straight cable with an effective prestressing force of 250 kN located at an eccentricity of 40mm. The beam carries a live load of 1.2 kN/m all over it’s span. Calculate
[7 marks]Top and bottom fiber stresses at center of span. Density of concrete = kN/m3. ii)Find Magnitude of Prestressing force with an eccentricity of 40mm which can balance the stresses due to dead and live loads at the bottom fibre of the central section of the beam.
[ marks]Explain with sketch IS 1343 (2012) recommendations for computing the Moment of resistance of rectangular section.
[3 marks]Enlist the formula for calculation of Moment of resistance of Flanged sections as per IS 1343 (2012) recommendations
[4 marks]Enlist the formula for calculating losses due to Elastic deformation and Friction in prestressed concrete sections2
[3 marks]Define transmission length, and what is expression of it as per IS 1343 (2012) recommendations.
[4 marks]Abonded prestressed concrete beam is of rectangular section of width 400mm and overall depth 1200mm. The tendons consisting of 3300 mm2 of standard strands with characteristic strength of 1700 N/mm2. The strands are located at 870 mm from the top face of the beam. The characteristic cube strength of concrete is 60 N/mm2. Estimate the ultimate moment capacity of section using IS 1343 (2012) recommendations.
[7 marks]Enlist various loads acting on bridges.
[3 marks]What are the advantages of Composite construction with prestressed and in situ concrete for structural members.
[4 marks]The cross-section of a symmetrical I-section prestressed beam is 300mm by 750mm (overall), with flange and web 100mm thick. The beam is post- tensioned by cables containing 48 wires of 5mm diameter high-tensile steel wires at an eccentricity of 250mm. The 28- days strength of concrete in compression is 40N/mm2. Assuming that the grouting of the tendons is 100 percent effective, determine the ultimate moment of resistance of the section using IS 1343 (2012) recommendations.
the beam is pre-tensioning ii) the beam is post-tensioning If the concrete undergoes a further shortening due to creep and shrinkage while there is a relaxation of 6% of stress in steel Modular ratio: E = 210 kN / mm2 s Anchorage slip = 0.8mm Friction coefficient of wave effect = 0.002 / m Creep coefficient, ф = 1.6 Total residual shrinkage strain = 300 x 10-6 for pre-tensioning and 200 x 10- 6 for post-tensioning
[6 marks]An Unsymmetrical Isection has an overall depth of 2000mm. The top flange width and depth are equal to 1200mm and 300mm respectively, and the bottom flange width and depth are equal to 750mm and 200mm respectively. The thickness of the web is 300mm. The tendons having a cross sectional area of 7000mm2 are located at 200mm from soffit of the beam. If the ultimate compressive strength of concrete and tensile strength of steel are 42 and 1750 N/mm2 respectively, and the tendons are effectively bonded to concrete, Estimate the Flexural strength of the section using IS 1343 recommendations.
[7 marks]